JP2011080944A - X-ray ct apparatus - Google Patents

Abstract

In inspection of an object such as a circuit board in which a plurality of specific parts such as solder balls such as BGA and CSP exist along the surface of the object or along the plane, cutting by a plane in which the solder balls are arranged An X-ray CT apparatus that eliminates the need for setting work is provided.
A plurality of preset specific singularities existing along a plane on or in the surface of a target object from three-dimensional image information of the target object W obtained by backprojecting projection data obtained by CT imaging. A singular part image array plane calculation means for finding a plane P through which the center of the image of each singular part passes and a tomographic image sliced on the plane P is automatically created by creating a slice image based on the three-dimensional image information. By providing display means on the display, it is possible to immediately display a tomographic image sliced on a plane on which solder balls or the like are arranged without requiring an operator to set the slice position.
[Selection] Figure 2

Description

  The present invention relates to an industrial X-ray CT apparatus, and more particularly to an X-ray CT apparatus effective for inspection of circuit boards and the like.

  In an industrial X-ray CT apparatus, generally, a sample stage for placing an object is provided between an X-ray source and an X-ray detector, and a pair of X-ray source and X-ray detector, a sample stage, Is rotated relative to each other, and after taking an X-ray projection data of the object at every predetermined minute angle, the X-ray projection data is subjected to a reconstruction operation such as a back projection process to obtain a tomographic image of the object. Get image information.

  In a so-called cone beam CT apparatus that generates cone beam X-rays from an X-ray source and detects them with a two-dimensional X-ray detector, reconstruction is performed using X-ray projection data collected by one imaging. By the calculation, three-dimensional image information of the object is obtained.

  Surface rendering method and volume rendering method are known as methods for displaying 3D image information of an object, but MPR (Multi Planar Reconstruction) display function, in other words, arbitrary section reconstruction function, or multi-section conversion function. A function called a display function or the like is often used (see, for example, Patent Document 1).

  The MPR display function is a function for displaying a plurality of tomograms cut along a plurality of planes, and not only a tomogram (horizontal tomogram) along a slice plane orthogonal to the central axis of the relative rotation described above, but also an arbitrary slice. This is a function for displaying a tomographic image along a plane, for example, displaying a tomographic image along a plane designated by an operator using a line cursor or the like on a horizontal tomographic image of an object already displayed. it can.

JP 2008-304422 A

  By the way, the X-ray CT apparatus having the MPR display function as described above is often used for inspection of a circuit board on which a BGA (Ball Grid Array) or a CSP (Chip Size Package) is mounted. In BGA and CSP, a large number of solder balls are provided on the surface of a substrate. In the inspection of these solder balls, each solder ball is in a plane passing through the center of each solder ball, that is, a plane parallel to the substrate. It is usual to display a tomographic image obtained by cutting the line. For this purpose, the operator sets a plane passing through the approximate center of each solder ball as a cut surface by a manual cursor operation.

  Here, CT imaging of a circuit board is usually performed in a state where the circuit board is placed on a sample stage using an appropriate jig, viscosity, or the like, so that the circuit board is not reliably in a state along the rotation axis. Therefore, it is necessary to perform the setting operation of the cut surface described above for each circuit board, and there is a problem that the work is troublesome.

  The present invention has been made in view of such circumstances, and an object such as a circuit board in which a plurality of specific parts such as solder balls, such as BGA and CSP, exist along the plane inside or inside the object. In this inspection, it is an object of the present invention to provide an X-ray CT apparatus that eliminates the need for setting the cut surface as described above.

  In order to solve the above-mentioned problems, the X-ray CT apparatus of the present invention is provided with a sample stage for placing an object between an X-ray source and an X-ray detector arranged to face each other. X-ray projection data at a plurality of projection angles acquired by rotating the X-ray source, the X-ray detection pair, and the sample stage relative to each other while irradiating an object on the sample stage with X-rays from the source is reproduced. By configuring, in the X-ray CT apparatus for constructing the three-dimensional image information of the target object, a plurality of preset specific parts existing along the plane on the surface or inside of the target object from the three-dimensional image information. A unique part image arrangement plane calculating unit that searches for an image and obtains a plane through which the center of the image of each specific part passes, and a tomographic image sliced by the obtained plane is automatically created based on the three-dimensional image information. On the display Characterized by that it comprises a display means (claim 1).

  Here, in the present invention, as a specific configuration example of the specific part image arrangement plane calculation unit, the three-dimensional image information is binarized and corresponds to a plurality of specific parts preset from the binarized image. Singular part image extracting means for extracting an image of a specific shape to be obtained, centroid calculating means for obtaining the centroid of each of the extracted singular part images, and plane calculating means for calculating an optimum plane passing through each calculated centroid position The structure (Claim 2) which consists of these can be employ | adopted.

  In addition, the X-ray CT apparatus of the present invention displays a tomographic image cut at a plurality of planes from the three-dimensional image information and also displays a tomographic image cut at a plane designated on any one of the tomographic images. A configuration in which a tomographic image cut by a plane obtained by the specific part arrangement plane calculating unit is one of the initial display tomographic images of the MPR display function (Claim 3). Can be adopted.

  The present invention solves the problem by displaying a tomographic image obtained by the apparatus automatically calculating a plane in which specific parts such as solder balls are arranged and cutting the plane.

  In other words, when a target is a circuit board with a BGA or CSP, for example, where there are unique parts that can be distinguished from other parts, such as solder balls, for example, it is obtained by CT imaging and reconstruction calculation. From the three-dimensional image information of the target object, a plane in which specific parts such as solder balls are arranged is automatically obtained, and a tomographic image cut along the plane is displayed on the display. Thereby, after the CT imaging and the reconstruction calculation are completed, the operator displays a tomographic image cut along a required plane without setting a plane to be cut.

  The method of calculating the plane in which the singular parts are arranged is set in advance from the binarized image obtained by binarizing the three-dimensional image information of the object obtained by the reconstruction calculation as in the invention according to claim 2. A method of extracting images of specific shapes corresponding to a plurality of specific parts, calculating the centroid of each extracted specific part image, and calculating the optimum plane passing through each centroid, for example, the sum of the distance from each centroid to the plane is A method of calculating a plane that is the smallest can be employed.

  In the apparatus having the MPR display function, the tomographic image cut along the plane obtained as described above is used as one of the initial display images, so that the inspection of a solder ball such as a BGA is immediately performed. It becomes possible.

  According to the present invention, when an object having a plurality of specific parts that can be distinguished from other parts such as a solder ball is present in a planar shape, such as a circuit board equipped with a BGA or a CSP, Since the tomographic image along the plane in which the parts are arranged is automatically displayed, it is possible to simplify the operation in the inspection of such an object. Further, since it is not necessary to involve the operator in determining the required tomographic image, it can be expanded to an inline device or the like.

  Further, in the apparatus having the MPR display function, as in the invention according to claim 3, by setting the tomographic image cut along the plane obtained as described above as one of the initial display images, Based on a tomographic image including a cross section of a specific part such as a plurality of solder balls, it is possible to perform a quick inspection such as displaying a tomographic image obtained by further cutting an abnormally suspected specific part at an arbitrary plane. .

In the configuration diagram of the embodiment of the present invention, a schematic diagram showing a mechanical configuration and a block diagram showing a system configuration are shown together. It is a flowchart which shows the example of the operation | movement procedure of embodiment of this invention. It is a figure which shows the example of the tomogram initially displayed after CT imaging | photography in embodiment of this invention.

DESCRIPTION OF SYMBOLS 1 X-ray generator 2 X-ray detector 3 Sample stage 4 Computer 5 Operation part 6 Display 7 X-ray controller 8 Axis control part R Rotation axis W Target object

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration diagram of an embodiment of the present invention. An X-ray generator 1 is arranged so that an X-ray optical axis thereof faces in the horizontal direction, and faces the X-ray generator 1 in the horizontal direction. An X-ray detector 2 is provided. And between these, the sample stage 3 for mounting the target object W is provided. In this example, the sample stage 3 rotates around a vertical rotation axis R orthogonal to the X-ray optical axis. In addition, the sample stage 3 can be moved in three orthogonal directions including the X-ray optical axis by driving a moving mechanism (not shown), and an imaging magnification, an imaging range, and the like can be set by this movement. . The X-ray generator 1 generates cone beam X-rays, and the X-ray detector 2 is a two-dimensional X-ray detector.

  In CT imaging, the sample stage 3 is rotated while irradiating the X-ray from the X-ray generator 1 toward the object W, and the output of the X-ray detector 2 is collected by the computer 4 at every minute rotation angle. Is done by. The computer 4 performs preprocessing on the output of the X-ray detector 2 collected, that is, X-ray projection data, as will be described later, and then calculates the three-dimensional image information of the object W by back projection processing. Store it on the hard disk.

  An operation unit 5 including a keyboard, a mouse, a joystick, and the like is connected to the computer 4. By operating this operation unit 5, any arbitrary 3D image information of the object W is stored. The tomographic image along the plane is displayed on the display 6 as MPR. In this embodiment, the computer 4 performs an operation when inspecting an object in which specific parts are arranged in a plane, for example, an object in which a plurality of solder balls are arranged in a plane, such as a BGA or a CSP. By setting the shape of the specific part, for example, a sphere in the case of a solder ball, by operating the unit 5, the plane on which the solder ball is arranged is automatically calculated, and the slice sliced on that plane The image is displayed as one of the initial images of MPR display.

  The computer 4 is also under control of an X-ray controller 7 that controls a tube current and a tube voltage to be supplied to the X-ray generator 1, and a rotating mechanism and a moving mechanism of the sample stage 3 are also provided. Control is performed via the axis control unit 8. Such commands and settings relating to control can also be performed by operating the operation unit 5 described above.

Next, the operation of the embodiment of the present invention will be described with reference to the flowchart of FIG.
CT imaging is started with the object W mounted on the sample stage 3. During CT imaging, the output of the X-ray detector 2 is taken into the computer 4 at every minute rotation angle of the sample stage 3 and stored in the memory or hard disk as X-ray projection data at each projection angle.

  When CT imaging is completed, each X-ray projection data stored in the memory or the hard disk is read out, subjected to preprocessing, and then subjected to back projection processing. The preprocessing includes sensitivity correction, distortion correction processing, filter processing, and the like.

  The three-dimensional image information of the object W obtained by the back projection process is stored in the memory of the computer 4 or the hard disk. The three-dimensional image information is binarized using a preset threshold value to obtain a three-dimensional binarized image.

  Next, an image of a specific part having a specific shape set in advance is extracted from the binarized image. For example, in the inspection of a solder ball on a circuit board including BGA, CSP, etc., a solder ball is set as a specific part, and a spherical shape is set as the specific shape. With this setting, a spherical or nearly spherical image, and thus an image of a solder ball in the circuit board, is extracted from the binarized image.

  Next, the three-dimensional coordinates of the center of gravity of each image of the extracted solder balls are calculated. Then, a plane P passing through each calculated center of gravity is calculated. The calculation of the plane P can be obtained by a known method such as obtaining a plane that minimizes the sum of the distances from the centers of gravity. Here, for example, in BGA and CSP, since the solder balls are arranged on the substrate surface, the plane P calculated as described above is a plane parallel to the substrate surface and passing through substantially the center of each solder ball. It becomes.

  The tomographic image sliced along the plane P passing through the center of gravity of each solder ball calculated in this way is one of the initial images of MPR display, that is, among a plurality of tomographic images displayed first after CT imaging. As one of them. That is, the MPR display parameters are calculated from the calculated formula of the plane P, the calculated parameters are set in the display software for MPR display, and the tomographic image sliced on the plane P is displayed.

  Examples of the initial image in this embodiment are shown in FIGS. 3A is a horizontal tomographic image CH cut at a preset vertical position, and FIG. 3B is a vertical tomographic image CV cut at a preset horizontal position, where (C ) Is a tomographic image CP cut along the plane P described above, and these tomographic images are simultaneously displayed on the same screen of the display 6.

  On each tomographic image screen, cursors Ch, Cv and Cp corresponding to slice planes of other tomographic images are displayed. That is, a cursor Cv representing the slice position of the vertical tomographic image CV and a cursor Cp representing the slice position of the tomographic image CP sliced on the plane P are displayed on the horizontal tomographic image CH. A cursor Ch representing the slice position of the tomographic image CH and a cursor Cp representing the slice position of the tomographic image CP are displayed. On the tomographic image CP, a cursor Ch representing the slice position of the horizontal tomographic image CH and a vertical tomographic image are displayed. A cursor Cv representing the slice position of the image CV is displayed.

  By displaying such MPR display first after CT imaging, the operator can immediately determine the presence or absence of a defect in the solder ball while viewing the tomographic image CP. In addition, by moving the cursors Ch and Cv as necessary on the tomographic image CP, a tomographic image of the other surface of the solder ball of interest can be displayed, so that an accurate inspection can be performed.

  As described above, the operator does not need to manually set a plane along the arrangement of solder balls as in the prior art, in other words, a plane parallel to the substrate, and a plane passing through the substantially center of each solder ball. Operation can be simplified.

  In the above embodiment, an example in which the sample stage 3 is rotated with respect to the X-ray generator 1 and the X-ray detector 2 has been shown. However, the X-ray generator 1 and the X-ray detector 2 A structure in which the pair is rotated around the sample stage may be used.

Claims (3)

A sample stage for placing an object is provided between an X-ray source and an X-ray detector arranged to face each other, and the object on the sample stage is irradiated with X-rays from the X-ray source, X-rays for constructing three-dimensional image information of an object by reconstructing X-ray projection data at a plurality of projection angles acquired by relatively rotating the X-ray source, the X-ray detection pair and the sample stage. In CT equipment,
From the above three-dimensional image information, search for images of a plurality of predetermined specific parts existing along the plane on the surface or inside of the object, and calculate a specific part image array plane to obtain a plane passing through the images of the specific parts An X-ray CT apparatus comprising: means; and display means for creating a tomographic image sliced at the obtained plane based on the three-dimensional image information and automatically displaying the tomographic image on a display.   The peculiar part image arrangement plane calculating unit binarizes the three-dimensional image information, and extracts a peculiar part image extracting unit that extracts images of specific shapes corresponding to a plurality of peculiar parts set in advance from the binarized image. 2. A centroid calculating means for obtaining the centroid of each extracted unique part image, and a plane calculating means for calculating an optimum plane that passes through the calculated centroid positions. X-ray CT apparatus described in 1.   The X-ray CT apparatus according to claim 1 or 2 displays a tomographic image cut along a plurality of planes from the three-dimensional image information, and a tomogram cut along a plane specified on any one of the tomographic images. An XR display function for displaying an image, and a tomographic image cut by a plane obtained by the specific part arrangement plane calculating means is one of the initial display tomographic images of the MPR display function Line CT device.

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